So the beauty of ITIL is that it is not a standard, just a framework. So there is no requirement to implement all the processes or the roles. You can pick and choose what works for you. However, what I can tell you is that ITIL is probably best rolled out in small chunks and for most organizations, it would be beneficial to send ost people to Foundations training and hire a consultant for implementation plans.
There is another similar framework I have been researching a lot lately and it is called FiTSM. I have a post coming in the near future on it. It is basically "ITIL Light" and more geared for smaller organizations.